The present invention relates to a chain tensioner.
Different types of chain tensioners have been proposed for providing the adequate tension to a chain. One of such chain tensioners is disclosed, for example, in JP-B2 No. 60-527, published on Jan. 8, 1985 in Japan.
JP-B2 No. 60-527 discloses a chain tensioner as shown in FIG. 6. Referring to FIG. 6, an engine cylinder block 64 is formed with a through bore 65. The chain tensioner includes a body 63 received in the bore 65 from the outside of an engine, a plunger 61 which is slidably received in the body 63, and a spring 62 for biasing the plunger 61 in such a direction as to protrude from the body 63.
An end portion of the plunger 61 protrudes inside the engine so as to press a chain (not shown)through a slide member (not shown). The tension of the chain is adjusted to an appropriate value by a force of spring 62.
JP-B2 No. 58-17891 discloses a chain tensioner. This chain tensioner comprises a body formed with a cylindrical bore having one end closed, and a plunger slidably received in the cylindrical bore. The plunger defines within the cylindrical bore a variable volume chamber. The body is formed with a recess serving as on oil reservoir. The body is provided with a one-way passage which allows a one-way flow of oil from the oil reservoir to the variable volume chamber. A flow restrictor is mounted in a passage formed through the body to restrict flow of oil from said variable volume chamber to the oil reservior. The oil within the oil reservoir is subject to atmospheric pressure. A spring is disposed within the body to bias the plunger in a direction to protrude from the body.
A problem encountered in the chain tensioner disclosed in JP-B2 No. 60-527 is that noise due to vibration of the chain is produced in expanding and contracting the spring 62 when the tension of the chain periodically varies with the variation of engine speed.
Another problem encountered in the chain tensioner disclosed in JP-B2 No. 58-17891 is although noise due to vibration of the chain is restrained by the presence of the oil reservoir, a restraint of noise is not sufficient that if the oil reservoir is small in capacity. On the other hand, in order to obtain sufficient restraint of noise, the oil reservoir should be larger, resulting in increase in size of the chain tensioner and/or difficulty to find a space or area for the oil reservoir.